Cooling towers are in wide use in industry. These towers are typically used to receive a warm or relatively warm fluid, such as, for example, warm water from an industrial operation. The warm water is passed through the tower and, by a heat exchange interaction with ambient air that is cooler than the water, the water is cooled and then can be discharged or returned to the industrial operation. Cooling towers include various configurations such as cross-flow cooling towers in which the air enters from a side of the tower and passes generally laterally horizontally across the fill media, and also counterflow cooling towers where the air generally enters beneath the fill material and is drawn upward through the fill material.
There are at least two general types of such cooling towers. The first general category includes evaporative type systems in which the water enters the top of the tower and falls through the tower while interacting with splash bars and/or sheet fill packs, also referred to herein as wet media. The water itself thus has contact with the ambient air and is cooled by its contact with the air, and then is collected in a lower collection basin. Evaporative cooling towers can take many configurations, and typically utilize a fan to move air through the tower and past the liquid being cooled, although natural draft cooling towers without fans are also known.
In evaporative cooling towers, depending on the operating and ambient conditions, some of the water will tend to evaporate and exit the tower with the exiting air. In some cases, the water vapor may exit the tower in the form of a visible water vapor or plume which is sometimes considered undesirable depending on location and other circumstances.
Another general category of cooling towers is closed circuit or dry cooling towers. A dry cooling tower contains the liquid to be cooled inside a conduit and air interacts with the conduit material and thus cools the liquid. The dry approach has the advantage that there is no evaporation into the cooling air and thus no plume. However, depending on the operating and ambient temperatures, in some cases dry cooling can be less efficient than wet cooling in terms of the energy consumption and/or construction expense of the tower. Moreover, dry cooling tends in some circumstances to be more dependent on the ambient temperature, and thus less suitable for climates where the weather and ambient temperature change through a wide range. Dry cooling towers can also use one or more fans or can be natural draft.
There are also known so-called hybrid towers which pass the fluid through a combination of evaporative and dry heat exchangers. In the prior art these combination or hybrid cooling towers have operated in a single mode where the water passes serially through one type of heat exchanger media (wet or dry) and then is recollected and passes through a second different type of heat exchanger media (wet or dry). The water travels serially through the two heat exchangers. Turning to air flow, it has been known to arrange the media so that each heat exchanger is contacted by its own air path. That is, the air paths through the two types of heat exchangers are separated from each other, at least to some extent, and thus the air itself passes through one or the other media section in a parallel fashion. In the parallel fashion of air flow, one air stream passes through one media and a second different air stream passes through the other media. It has been known to subsequently mix these two air streams for discharge from the tower. A potential difficulty in operating and designing such hybrid systems is that the optimum configuration for reducing plume is dependent on the operating and ambient temperatures, and when these temperatures vary, for example due to seasonal changes, there can be too much plume, or less than optimal efficiency.
Accordingly, it would be desirable to have a cooling tower that can provide desirable efficiencies while also reducing plume.